1. Field of the Invention
The present invention relates to an optical apparatus, and more particularly to an optical apparatus including a detector that detects rotation of a drive member to drive an optical element.
2. Description of the Related Art
Japanese Patent Laid-open No. 2014-35438 discloses a lens apparatus which is provided with a constant position guide roller mechanism to remove backlash between a drive ring and a drive base so that rotation of the drive ring to drive a focus lens can be detected by a detection system using a scale and a sensor with high accuracy.
However, the configuration disclosed in Japanese Patent Laid-open No. 2014-35438 is not concerned about the deterioration of position detection accuracy when an abutting portion of a connection key, which is attached to the drive ring to transmit rotation to the lens unit, strikes on a rotation end of the drive base in manual focusing. Commonly, a mechanical end as a drivable range in the manual focusing, which is limited by the rotation end of the drive base, is set with a margin compared to an electric end as a rotational range where autofocus driving is possible, and an angular position away from the mechanical end by a certain angle is set as the electric end. In other words, the rotational range in the autofocusing is set so as not to strike on the rotation end of the drive base. When the drive ring rotates and the abutting portion of the connection key strikes on the rotation end of the drive base in the manual focusing, due to a rotation moment, the drive ring operates to further rotate to be decentered around a contact portion, as a rotation center, between the abutting portion of the connection key and the rotation end of the drive base.
An inner surface of the drive ring is supported by a plurality of guide rollers, and at least one of the guide rollers is a biasing guide roller that is biased by a bias spring to bias the drive ring in an outer radial direction. Since this biasing guide roller is disposed in a region where the drive ring is decentered to sink in an inner radial direction due to the rotation moment according to further rotation of the drive ring, the decentering caused by further rotation of the drive ring cannot be suppressed. Although the connection key is stopped and a lens unit fitted in its front edge is also stopped, only the drive ring further rotates and the lens unit is moved as a detected value, and as a result, an actual lens position is different from a detected position (the detected value) and thus detection accuracy is negatively affected.
Position information of the mechanical end may be obtained based on a result of driving a manual focus drive region, but the drive ring is at risk of striking on the mechanical end as the rotation end of the drive base at the position of the electric end for the focus drive when the lens position is different from the detected value described above. In order to avoid such a risk, a biasing force of the bias spring to bias the biasing guide roller can be increased to endure the rotation moment. However, the drive ring is deformed by increasing the biasing force and thus the position detection accuracy may be deteriorated. In addition, a load is increased and thus sliding of the drive ring may be deteriorated.